In order to securely perform Internet communications between a Web server and a Web browser, SSL (Secure Socket Layer) using PKI (Public Key Infrastructure) has been put to practical use. In a communication system in which the SSL has been introduced, since an encryption process is performed by using a server certificate (SSL certificate) issued by a certificate authority (CA) which is a trusted third-party authority, spoofing, tamper, sniffing and the like are prevented and more secure Internet communications are assured.
When the certificate authority issues the server certificate, authentication of a person requesting the issuance of the server certificate is important. As a authentication method, a server certificate issuing system using domain authentication has been put to practical use (for example, see Patent Document 1). In this known authentication method, when the issuance of a server certificate is requested, a registration server accesses a database of a domain registration authority (Whois information) to contact an approver having an authority to approve the issuance of the server certificate for the above described Web server. Using communicating means such as telephone, e-mails or the like, whether or not the certificate request is approved is verified, and only if the approval from the approver is obtained, the certificate is issued.